Research on the Virulence Identification and Preservation Methods of Desert-type Leishmania donovani Strains

ObjectiveTo determine the virulence of desert-type Leishmania donovani strains through animal infection experiments and to explore preservation methods for maintaining their pathogenicity. Methods The isolated strain was cultured in vitro for 7, 30, 36, 44, 60, 90, and 150 days, respectively， and inoculated into Lagurus lagurus (L.lagurus) with the dose of 2.6×105 per animal by intraperitoneal injection. The spleen coefficient, infection rate, and antibody positive rate of the inoculated animals were detected at day 60 after infection. The desert-type Leishmania donovani strain was further inoculated with Cricetulus migratorius (C.migratorius) and L. lagurus, respectively, for passaging and preservation. The survival time of two kinds of animals and pathogenicity change of the stain in their bodies were compared. Results After inoculation of desert-type Leishmania donovani strains cultured in vitro for 7-150 days, the spleen coefficient of inoculated L.lagurus gradually increased from 1% on day 7 to 2.2% on day 30, which was more than 10 times of the normal spleen coefficient. Additionally, on day 60, the spleen coefficient remained 3 times higher than the normal value. The infection rate and antibody positive rate decreased from 80% on day 7 to 0% on day 60. At 90 days, there were no significant differences between the infected groups and the control group, and all the observed indexes were within the normal range. The survival time of L.lagurus infected with the in vivo passage strain ranged from 1 to 13 months, and half of the infected individuals died within 4 months. In contrast, C.migratorius had a survival time ranging from 5 to 31 months, and half of the infected individuals died within an average of 13.7 months. There was a significant difference in the average time of death between the two groups (t=0.000 1, P<0.001), but no significant difference in spleen coefficient (t=0.990, P>0.05). This strain exhibited equal virulence in both animals and remained virulent for up to 4 years after continuous passage. ConclusionWith the prolonged culture time, the virulence of the strain decreases gradually. At 90 d, it has no pathogenicity to L. lagurus. Long-term in vitro culture fails to preserve it's pathogenicity to L.lagurus. Only in vivo inoculation can maintain the virulence of this strain.